What is Responsive Web Design?

Responsive web design (RWD) is an approach to web design aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from desktop computer monitors to mobile phones)

Cheat Sheet
Using the responsive web design cheat sheet is very simple.Find the device you’re designing for on the chart and read what breakpoint dimensions it should have – and there you have it.